This invention relates to an improvement in flank relief to correct for rotational misalignment on non-constant generating radius scroll compressor wraps.
Scroll compressors are becoming widely utilized in refrigerant compression applications. As known, scroll compressors include two scroll members each having base and a generally spiral wrap extending from the base. The two spiral wraps interfit to define a plurality of compression chambers. One of the scroll members is driven to orbit relative to the other. In one type scroll compressor, both members orbit and this invention also extends to this type compressor. As the two scroll members orbit relative to each other, the size of the chambers between the scroll wraps are decreased to compress an entrapped fluid.
Traditionally, scroll compressors have had their spiral wraps formed as involutes of a circle. These spiral wraps have a constant generating radius, and thus expand ever increasingly from a common center. These traditional scroll wraps have typically also had constant thicknesses for the wraps. Much of the early design of scroll compressors relied on a model of an idealized scroll wherein the two scroll wraps were perfect involutes, and were both perfectly centered about a common center. However, manufacturing tolerances and variations often result in imperfections, especially near the beginning and ending points of the scroll wraps. These imperfections cause one of the scroll wraps to contact the other scroll wrap prior to the remainder of the scroll wrap coming into contact. That is, due to imperfections in the manufacturing process, there has sometimes been inadvertent contact. This has resulted in undesirable noise.
The prior art has attempted to address this problem by forming a relief in the flanks of the scroll compressors at either the beginning and/or ending points of the wraps. This causes these regions which formally contacted prior to the remainder of the scroll wrap coming into contact, to instead contact at about the same time or even after the remainder of the scroll wrap comes into contact. This process reduced or eliminated the inadvertent contact and correspondingly reduced undesirable noise.
For the traditional scroll wraps which are based on involutes of a circle and which have a constant pitch, or spacing, between successive wraps, rotational misalignment of the two scrolls does not usually cause difficulty with inadvertent contact and any associated undesirable noise. Because successive wraps have equal spacing, i.e., constant pitch, any relative rotation of the wraps causes an equal error to be introduced at each contact point between the wraps and thus the relative contact between wraps is unchanged. Normally, the only problem associated with relative rotation between the wraps is loss of performance as the induced error in contact points causes one set of points to open up to form clearances through which compressed vapor can leak.
More recently, scroll compressor designers have achieved increased operational benefits by scroll wraps which are not formed on an involute of a circle.
As examples, hybrid scroll wraps and high order scroll wraps are often utilized in modern scroll compressors. In these scroll compressors, there is not a constant generating radius along the entire wrap. Some of the scroll wraps are formed of several segments each formed on a circular arc. The segments are connected together to form an entire wrap. However, across the wrap the generating radius changes. Further, other types of scroll wraps have varying generating radiuses, and varying profiles.
When rotational misalignment occurs with non-uniform generating radius scroll compressors, the initial contact point during rotational misalignment moves. It is no longer necessarily at the beginning or end of the wrap. It may also move instantaneously from one portion of the wrap to another during operation, thus causing a series of inadvertent contacts. This multiplies the potential for undesirable noise. Thus, the above discussed solution is not applicable to scroll compressors having a non-uniform generating radius.